Electrical contacts and connectors, as used in the electronics field, are generally fabricated from copper alloys onto which is electrodeposited a thin layer of a precious metal such as gold or palladium. The electrodeposit must possess certain metallurgical properties such as corrosion resistance, freedom from porosity, wear resistance, low and stable contact resistance, ductility, etc. In most cases, gold which has been hardened with a small amount of nickel or cobalt is used as the electrodeposit.
The industry initially began to substitute palladium or palladium alloys in place of gold in an attempt to lower the cost of these contacts. Thus, the industry is continually searching for better electroplating baths and processes for depositing these metals.
Numerous electroplating solutions for pure palladium have been disclosed by the prior art. Although these solutions may contain various palladium species, a wide range of additives, and pHs ranging virtually from 0 to 14, the most commonly employed palladium plating solutions contain inorganic amine complexes of palladium. Two preferred complexes are palladosamine chloride Pd(NH.sub.3).sub.4 Cl.sub.2 or palladium diaminodinitrite Pd(NH.sub.3).sub.2 (NO.sub.2).sub.2 and baths containing these complexes are usually operable over a pH range of between about 8 and 10. It is also common to utilize a slight excess of ammonia or ammonium hydroxide to stabilize these complexes in the bath.
Such prior art plating baths have several disadvantages, including evolution of ammonia fumes, frequent replenishment of the ammonium stabilizing compound and the required use of strike baths for certain basis metals.
The present invention proposes electrolytes and methods for the electrodeposition of pure palladium or palladium alloys that present an improvement over the prior art electrolytes and their deposits.